1. Field of the Invention
This invention relates to the transfer of water from bodies of water that are populated by live fish or particulate matter, or both. In particular, this invention addresses concerns encountered in the use of barrel-type fish screens that are designed to prevent fish and/or particulate matter from entering water intake vessels.
2. Description of the Prior Art
Water is often drawn from lakes, rivers, oceans, and other natural bodies of water for use by manufacturing plants, municipalities, irrigation systems, power plants, and other large operating facilities. Since these bodies of water typically support aquatic life that includes fish and other aquatic animals, screens commonly referred to as “fish screens” are commonly used to prevent the animals and particulate matter from entering the intake vessels through which the water is drawn and thus to prevent contamination and damage to units in the facilities such as pumping systems, deaeration systems, and the like. The fish screens also preserve the viability of the aquatic animals and prevent them from injury, thereby helping to maintain the ecosystem in the body of water.
A common form of fish screen is the “barrel-type” screen which is a cylindrical screen mounted to the water intake vessel, which is typically a pipe, the screen and pipe being coaxial and joined together at one end of the cylinder. Water enters the screen through the sides of the cylinder and travels axially within the cylinder before entering the pipe, while the fish are kept outside. Within the cylinder and prior to entering the pipe, the water passes through a collection manifold, which is a perforated and truncated cone that extends the length of the cylinder with the widest end of the cone at the location of the pipe. The perforated cone serves as a flow modifier to even out the inflow of water along the axis of the cylinder, i.e., to achieve a uniform axial velocity of flow within the cone, independently of the total flow rate of water into the cylinder. Evening out the inflow in this manner is important both in avoiding trauma to the aquatic life in the surrounding water by spreading the inflow along the length of the screen, and in minimizing or preventing dead volume within the cylinder that create nonunifoimity of inflow along the cylinder length. Inflow nonuniformity nevertheless remains a challenge. Uniform and continuous flow also requires that the screen be kept clear of debris, including plant and animal debris and solid particulate matter in general that tend to collect on the outer screen surface and clog the screen openings. The cylindrical screen is typically supported over the perforated cone by an open rib structure, providing the entire fish screen with its barrel-type construction. The two opposing ends of the rib structure are secured to plates at the opposing ends of the perforated cone.